L0301P16 - Primary Tissue Types - Nerve and Muscle
Muscle Tissue Skeletal Muscle *also known as striated muscle *muscle fibres = muscle cells *contains myofibrils **comprises thick myosin filaments and thin actin filaments **interaction of the two myofilaments control the contraction of muscle ***they themselves do not alter in length, instead they slide over each other Abbreviations (for image right) *AX - axon *V - vesicles containing Acetylcholine (ACh) *S - sarcolemma (ACh receptors on it) *TT - transverse tubular system (T-tubules) *SR - sarcoplasmic reticulum Process of Contraction *action potential arrives at neuromuscular junction where neurotransmitters are released from vesicles at motor end plate *neurotransmitters bind to receptors on the sarcolemma causing depolarisation and action potentials spread along the muscle and down the T-tubules *sarcoplasmic reticulum stimulated to release calcium flooding the myofibrils and their sarcomeres causing contraction Sarcoplasmic Reticulum *modified endoplasmic reticulum *stores calcium ions Sarcomere *unit of contraction **shortens during contraction *runs between two Z lines Striations *caused by organisation of myofilaments *A band - anisotropic **broad and dark **where myosin and actin overlap *I band - isotropic **less dark **only actin filaments *perpendicular to the direction of muscle fibre Cardiac Muscle *also known as cardiomyocytes *have sarcomeres **similar to skeletal muscle with A (dark) and I (light) bands and Z lines *T-tubules and sarcoplasmic reticulum form dyads at the level of the Z line *cells are joined end-to-end by intercalated disks (only found in cardiac muscle) *abundant mitochondria – indicative of high aerobic metabolism *considered incapable of undergoing proliferation *communicate chemically via gap junctions Smooth Muscle *no striations but still rely on actin/myosin interactions for contraction *calcium dependent *muscle of the visceral organs **often part of the walls of hollow organs ***eg. intestines, stomach, uterus, bladder, arteries, veins *actin-binding dense plaques are present in sarcoplasm **plaques are the equivalent of Z lines in striated muscle *involuntary control *communicate with each by specialised gap junctions Nervous Tissue Central Nervous System *brain *spinal cord Peripheral Nervous System *everything else *consist of: **nerve cells (neurons) **supporting cells (glial cells or neuroglia) **blood vessels (contains other tissue within) Neuron *100 billion in the human nervous system *able to: **receive information from external or internal sources **process and integrate these signals **conduct nerve impulses (action potential) to designated target tissues *are: **excitable - responsive to change **conductive - transmit action potentials **secretory - communicate with other cells using chemical messengers *typical neutron consists of: **cell body (a.k.a soma, perikaryon) **multiple dendrites **one axon Parts of the Neuron Nissl Bodies *stacks of rough ER (lamellae) *highly synthetic cell Oligodendrocyte *glial cell of the CNS *synthesises the myelin sheath Schwann Cell *glial cell of the PNS *synthesises the myelin sheath Dendrites *short branched extension of nerve cell *receives impulses from other cells Axons *can be myelinated or unmyelinated **lipid sheath surrounding axons *unmyelinated cells still has the Schwann cell cytoplasm around axons **generally shorter axons Types of Neurons *motor (efferent) neurons **control effector organs such as muscle fibres and exocrine and endocrine glands *sensory (afferent) neurons **receive sensory stimuli from the environment and from within the body *interneurons **establish relationships between other neurons **form complex functional networks   Synapses *responsible for unidirectional transmission of nerve impulses *sites where contact occurs between neurons or between neurons and effectors *most transmit the nerve impulse by releasing neurotransmitters at the axon terminal *consists of: **axon (presynaptic) terminal ***contains synaptic vesicles with neurotransmitters, mitochondria and microtubules ***swelling of the end of axon = bouton **postsynaptic terminal **synaptic cleft  (right) *types: **axosomatic ***axon soma **axodendritic ***axon dendrite **axoaxonic ***axon axon